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Harbor Shield: Protecting Harbors From Hull-Mounted Explosives
U.S. Navy, Battelle Build a Side Scan Sonar System To Inspect Tanker Hulls for Terrorist Bombs and Other Contraband

By Mike Lafferty
Freelance Science Writer
Richard Granger
Harbor Shield Project Manager
Columbus, Ohio

Advances in cargo scanning technology have improved the ability of port security officials to inspect shipping containers for weapons of mass destruction and illegal imports. Inspecting cargo hull exteriors for explosives and other contraband, however, remains highly labor intensive. The current defense against such an attack requires divers to inspect each ship entering a harbor, a difficult, dangerous and time-consuming task.

Liquefied natural gas (LNG) tankers are of particular concern to officials across the United States, from the Port of Boston to the Port of Long Beach. Officials fear a terrorist attack on an LNG carrier could generate a devastating fireball, wrecking not only the port but also destroying neighborhoods for miles around, disrupting commerce for days or weeks.

To combat this danger, the U.S. Navy and Battelle (Columbus, Ohio) have been developing a sensor system that could guard high-risk ports. This sensor system, called Harbor Shield, scans ship hulls for explosive devices as well as illegal drugs and other contraband. The system went through testing in 2007 and is currently in a test deployment running from February through June.

Graphic representation of Harbor Shield in a harbor as it scans the hull of a passing ship.

Growth of Threat From LNG Tankers
LNG tankers have drawn increasing attention as a potential terrorist target in recent years, especially as the volume of natural gas imported to the United States by tanker has increased. There are five LNG port terminals in the United States, but as many as 40 more are being considered, several near highly populated areas.

The majority of natural gas is imported in tankers, which often carry about 30 million gallons of refrigerated, compressed fuel. LNG will not ignite in its compressed, refrigerated state, but if a bomb tore into a vessel's storage tank, the LNG released would boil into gas. Mixed with air, it would pose the threat of ignition and explosion.

A 2004 report from Sandia National Laboratories said that while most damage from an LNG explosion would be within several hundred yards, such an explosion could burn skin and damage buildings up to one mile away. The report characterized the threat as low, but it also said the potential damage is so catastrophic that LNG tankers should be prohibited from sailing near populated areas until sufficient protections are in place.

Additionally, the technology to discreetly attach a payload to a ship hull already exists. Drug enforcement officials have already discovered containers attached to the underwater hulls of ships to smuggle illegal drugs.

The Harbor Shield System
Harbor Shield, developed from a patent by Donald Steinbrecher at the Naval Undersea Warfare Center (NUWC) Newport, consists of a pair of transmitters and receivers set up on each side of a shipping channel. The sonar scans a ship's hull and the results are recorded. If anything looks suspicious, the ship can be stopped and inspected.

Advances in sonar technology, specifically advances in higher resolution and improved data-processing capabilities, have made Harbor Shield possible. The system, which was designed to accommodate existing vessel traffic patterns, only requires that ships stay in the channel between the scanners.

Harbor Shield relies on repetitive scanning of the same vessel, allowing the system to recognize anomalies or changes in the hull form. The idea is that a vessel routinely traveling between U.S. and foreign ports will pass through a Harbor Shield portal many times, with each visit being recorded and stored.

As a ship approaches a harbor, the vessel transmits a valid automatic identification system signature recognized by the U.S. Coast Guard's vessel-tracking program. This signal would alert the harbor control center to download and display previous hull scans of the ship. As the vessel approaches the port and enters the shipping channel, the sensor system scans the hull, adding data to a new composite.

This new hull print is then automatically compared to archived images. If a bomb were attached, Harbor Shield would recognize the difference. If a previous hull print were not available, the system would still be capable of identifying anomalies based on sonar imaging results and existing data for similar vessels.

While the Harbor Shield system's emphasis is on port protection, it could also be deployed at choke points such as the Panama Canal, Suez Canal, St. Lawrence Seaway and river mouths such as the Mississippi. The system's electronic library also makes Harbor Shield potentially useful for maintenance; hulls can be automatically examined for marine growth, corrosion and other problems.

At least initially, the system will be used primarily at naval bases to gauge performance. Both permanent and mobile versions could be developed.

Harbor Shield equipment in a warehouse before it was deployed in Narragansett Bay near Newport, Rhode Island, in late 2010.

Final Testing Set
The system was tested in Narragansett Bay near Newport, Rhode Island, for a month in 2007. Harbor Shield is now set for real-world testing from February to June at a natural choke point used by ships of more than 100 tons entering Narragansett Bay.

The latest test system will include two upward-looking commercial off-the-shelf side scan sonar modules that the team has modified. These modules have been installed several hundred feet apart in 70 feet of water on the floor of the channel. These will be connected to a receiving station at the nearby NUWC.

During the testing phase, data from ship traffic will be collected while vessels are in transit and then analyzed to evaluate the system's ability to image a variety of hulls in various environmental conditions. Scientists are not yet sure how small of an object could be detected, which is what the testing is designed to determine. The main objective during this testing will be to minimize false positives and false negatives.

The current system includes user interface software to display data in real time. Future versions of the system would include additional automated software features for enhanced decision support.

During testing, the operators will review its performance, collecting detailed data in a variety of weather and fine-tuning the system. For example, scientists want to check whether transmission and reception are degraded by the buildup of marine growth on the equipment.

During the 2007 test, biological fouling occurred on the sonar and its supporting hardware within a couple of weeks. The new test system has incorporated anti-biofouling mitigation techniques.

Commercial Deployment
Once Harbor Shield collects a sufficient amount of data, the system will be able to be commercially deployed. The current system could be used for extended field trials at various sites with minor modifications and, with some additional development, it could be deployed commercially within a few years. The Harbor Shield system offers the potential to provide new security data from a moving vessel that cannot be captured in any other way.

Mike Lafferty, a retired science writer for the Columbus Dispatch newspaper, is a freelance writer specializing in science, environment and education issues. He lives in Granville, Ohio.

Richard Granger is the project manager for the Harbor Shield program. He joined Battelle in 1999.

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